Complex dynamic restoration processes leading to a high degree of deformability in a dual-phase Al0.5CoCrFeNi high entropy alloy

Abstract

The current research provides scientific evidence based on experimental and modeling approaches that complex softening processes characterized by dynamic recovery (DRV) and dynamic recrystallization (DRX) combined with twinning contribute efficiently to the hot deformation processing of the Al0.5CoCrFeNi alloy. An as-cast face-centered-cubic (fcc) oriented Al0.5CoCrFeNi dual-phase high entropy alloy, HEA, was deformed in uniaxial compression to a true strain 0.8 at temperatures between 900 and 1100 ºC and strain rates from 0.0013 to 0.1 s−1. A dynamic material model was applied to predict the processing windows, and the underlying deformation mechanisms were characterized using scanning electron microscopy and electron backscattered diffraction. The optimum processing window for the studied alloy is at 900–960 ºC/ 0.0013–0.002 s−1, where the efficiency of power dissipation and strain rate sensitivity ranges from 45% to 50% and 0.28–0.33, respectively. The processing map also exhibits a domain of flow instability located in the lower temperature and higher strain rate regions, resulting mainly from flow localization. The studied alloy represents a dual-phase fcc + bcc/B2 microstructure in an as-cast (undeformed) state. The fcc matrix occupying 94 vol% forms dendrites with an average diameter of 210 µm, decorated by discrete networks of bcc/B2 phase of average grain size 3.5 µm residing in interdendritic regions. The microstructural analyses corroborate the coincidence of DRX and twinning in the fcc phase in all deformed specimens. However, only DRV takes place within the bcc phase. The current study reveals a well-suited parameter range to achieve a high degree of hot deformability in dual-phase HEAs by taking advantage of twinning combined DRX to refine the microstructure significantly. Future work will have to identify possible application cases.